Silver halide,heat-developable image sheet containing mercuric ion

ABSTRACT

A LIGHT-SENSITIVE HEAT-DEVELOPABLE IMAGING SHEET CONTAINING CATALYTIC AMOUNTS OF LIGHT-SENSITIVE SILVER HALIDE IN CATALYTIC ASSOCIATION WITH ORGANIC SILVER SALT OXIDATION-REDUCTION IMAGE-FORMING MEANS IS GIVEN INCREASED SPEED, STABILITY AND CONTRAST BY INCORPORATION OF MERCURIC ION.

June 29, 1971 s. P.'-B|RKELAND 3,539,993

' SILVER HALIDE HEAT-DEVELOPABLE IMAGE SHEET v CONTAINING MERCURIO ION June 29, 1971 s. P. BIRKELAND SILVER HALIDE HEAT-DEVELOPABLE IMAGE SHEET CONTAINING MERCURIC ION ,2 Sheets-Sheet 2 Filed Feb. 2s, 1968 I W m. A f L0 0 3 Mr V 5 A A Z f v 0 A l, Z fw W F f 7 0 m H 0 F M 5 7 2 l 0 a 0 W M M M M n u m h @u Qmuw RQ MQ United States Patent O U.S. Cl. 96-67 10 Claims ABSTRACT OF THE DISCLOSURE A light-sensitive heat-developable imaging sheet containing catalytic amounts of light-sensitive silver halide in catalytic association with organic silver salt oxidation-reduction image-forming means is given increased speed, stability and contrast by incorporation of mercuric ion.

This invention relates to the visible recording of lightimages and to light-sensitive and heat-developable sheet materials useful therein.

In U.S. application Ser. No. 693,714 led Dec. 27, 1967, now U.S. Pat. No. 3,457,075, there is described a lightsensitive heat-developable sheet material containing a photosensitive silver halide in catalytic association with an image-forming oxidation-reduction reaction mixture of organic silver salt and reducing agent. Exposure of the sheet to a light-image results in the formation at the lightexposed areas of a catalyst which accelerates the heatreaction of the silver salt mixture, the latter then on subsequent heating undergoing accelerated reaction at the catalyzed areas to develop a corresponding Visible image.

It has now been found that sensitive sheet materials of the class indicated may be significantly improved in a number of respects by the incorporation in the sensitive layer of sources of small but highly significant amounts of mercuric ion. As an example, the invention has made possible the recording of cathode ray tube single field exposures on photosensitive heat-developable dry silver sheet material.

The mercuric ion may be introduced in any desired manner. A mercuric compound may be added to the coating composition containing either the organic silver salt, or the reducing agent, or both; or it may be applied as a separate coating. It has been found particularly convenient to introduce the mercuric ion in the form of mercuric halide under conditions which permit the halide ion to react with a small proportion of the organic silver salt to form the required photosensitive silver halide, the latter remaining in catalytic proximity with the remainder of the silver salt. Where other sources of halide ion are provided, the mercuric ion may be introduced in the form of compounds of anions other than the halide, for example acetate, behenate, benzoate, bromate, chromate, citrate, chloranilate, iodate, lactate, nitrate, oxalate, phthalate, salicylate, succinate, sulfate, or as mercury compounds of hexamethylenetetramine, pentachlorophenol, or phthalazinone. Any compound capable of providing mercuric ions in the system employed is operable in the practice of the invention; but compounds of extremely low solubility, or dark color, or Whose anions have a deleterious effect, such for example as mercuric sulfide or thiocyanate, will ordinarily be avoided.

As little as about 100 parts by weight of mercuric acetate per million parts of silver behenate half soap has been found to cause significant improvement in sheet materials as herein described, although larger amounts of about 300 to 5000 parts per million are generally preferred, and amounts of -up to 20,000 or more parts per million of the silver half soap have been found useful, These amounts 3,589,903 Patented June 29, 1971 ICC correspond to approximately .0004 to .07 mol of mercuric ion per mol of silver.

Silver behenate half soap is a mixture of equimolar proportions of silver lbehenate and behenic acid, obtained by precipitation with silver nitrate and nitric acid from the sodium salt of commercial behenic acid. Other ratios of silver salt and free acid may be used, or the free acid may be omitted, particularly where transparency is desired. Silver salts of other long chain fatty acids, e.g. silver stearate, may be used. Other organic silver salt oxidizing agents, e.g. silver p-hexoxybenzoate, silver octadecoxybenzoate, silver p-methoxycinnamate, which likewise provide a visible image on reduction, are also contemplated for use in this invention.

An important characteristic of the preferred sheet materials of this invention is their improved stability on prolonged aging prior to exposure and development. The sheet containing mercuric ion produces a substantially equally dense image but with a much lighter background than does a comparable sheet free of mercuric ion when both are stored, exposed, and developed under identical test conditions.

Sheet materials of this invention which contain Waterinsoluble sterically hindered normally solid o-alkyl substituted phenols or the like as reducing agents for the organic silver salt, and particularly those which additionally contain phthalazinone or equivalent materials, are found to have further advantages over sheets containing these same components but in the absense of mercuric ion. As one example the novel photosensitive heat-developable print papers of the invention containing these materials are found to possess a significantly higher photographic speed. For such papers the photographic speed may be defined* Where E is the exposure in meter-candle-seconds. Exposure and density values are obtained in accordance with Wellknown sensitometric principles, development in each instance bein-g accomplished by heating for the specified time at the speciiied temperature. Uniform heating is obtained by holding the sheet in uniform pressure-contact with the smooth surface of a uniformly heated drum or roller, or in any other equivalent manner.

Phthalazinone has previously been found to provide a toning action in copy-sheet coatings containing silver soap and reducing agent, as shown for example in U.S. Pat. No. 3,080,254. Although a similar effect is undoubtedly provided in the compositions of the present invention, an additional and apparently catalytic effect is also obtained whereby the hindered phenols, which otherwise react only with diliiculty with the silver ion, are enabled to react much more rapidly and effectively. The amount of phthalazinone may vary from about one-half to about ten percent of the total Weight of the coating.

Examples of solid Water-insoluble o-alkyl phenols which have been shown to be useful in these compositions include a number of compounds commercially available as anti-oxidant or preservative materials and identifiables as:

bis (2-hydroxy-3-tertiarybutyl-S-methylphenyl) methane;

bis (2-hydroxy-3,5-di-t-Ibutylphenl) methane;

2,4,4-trirnethyl-pentyl-bis-(2-hydroxy-3,5dimethyl phenyl) methane;

4,4methylenebis 3-methyl-5-t-butylphenol) bis (3-methyl-4-hydroxy-S-t-butylphenyl) sulfide;

4,4-rnethylenebis (2,6-di-t-butylphenol);

2,2-methylenebis (2-t-butyl-4-ethylphenol);

3,5-di-t-butyl-4-hydroxybenzyl-dimethylamine;

#As defined in ASA, pH 2.2 (1966).

2,6-methylene-bis 2-hydroxy-3 -t-butyl51nethylphenyl) 4-methyl phenol; ,u-(3,5-di-t-butyl-4-hydroxyphenyl) dimethylether; and 3,3',5,5tetra-t-butyl-4,4'dihydroxybiphenyl.

In the following illustrative but non-limiting examples, all proportions are in parts by weight unless otherwise indicated.

EXAMPLE 1 Composition A:

Silver behenate half soap 8.2 Zinc oxide 14.3 Polyvinyl butyral (binder) 7.0 Toluene 20.5 Acetone 50 Composition B:

Polyvinyl pyrrolidone (binder) 3.0 Ammonium bromide 0.075 Succinic acid .20 Hydro quinone 5 .25 Silica powder 2.0 88.5

Methyl alcohol sensitizing dye .0015 Acetone (solvent for dye) 2.93

The two compositions are prepared by mixing the components in a ball mill to provide a smooth mixture which spreads evenly under a knife coater.

In this example the sensitizing dye is 3-allyl-5-[3-ethyl (2 naphthoxazoylidene) ethylidene]-l-phenyl-Z-thiohydantoin. Other useful spectral sensitizers are listed in application Ser. No. 693,714.

Sensitive strips are prepared by coating paper with a iirst layer of composition A at 1.25 g./sq. ft. dry weight followed by a second layer of composition B at 0.30 g./sq. ft. dry weight. Additional strips are similarly prepared but with the addition of mercuric acetate to composition A, and also with the addition of phthalazinone to composition B. For most accurate comparison the strips are coated side-by-side in each test series and are then simultaneously exposed and developed under identical conditions in a Quadrant dry-silver printing machine, wherein development is obtained by contacting the back of the sheet for three seconds With the smooth surface of a metal drum maintained at 212i2 F. Density is determined at unexposed and at fully exposed areas with a reectometer. Density readings are recorded under D min. for the lightest and D max. for the heaviest density areas of each strip.

The iirst series shows the effect of mercuric acetate in suppressing the background darkening or fog obtained on sheets which have been subjected to accelerated aging prior to exposure, e.g. by holding in an oven for periods equivalent to several months of normal room-temperature aging. The image densities will be seen to remain essentially constant. The amount of mercuric acetate is shown as grams per 100 grams of composition A.

In a second series, 0.5% of phthalazinone is added to composition B (second layer) and a similar suppression of fog is achieved by incorporation of the mercuric salt in the rst layer.

TAB LE II El; after accelerated aging D max.

Hours at 140 F.

Mercurio acetate 0 1 2 3 4 5 6 TABLE III matter Wet heat aging D max.

Days at F. and 85% RH Mercurio acetate 0 6 16 26 The same type of improvement is experienced -with transparent coatings of unpigmented full silver soap compositions on transparent iilm backings, on the incorporation of mercuric ion.

EXAMPLE 2 In this example the halide ion is added in the form of calcium bromide to the rst coating composition and following the addition of the indicated amount of mercuric acetate. The two compositions are applied to paper at dry coating weights of 1.25 and 0.30 g./sq. ft. respectively as in Example 1. Prints are prepared by exposure at 300 foot-candles through a step wedge for 10 seconds and development at 235 F. for 25 seconds, and density measurements are obtained and reported as in Example 1 except that the density is given in terms of the range of readings for both the unexposed area (D min.) and the fully exposed area (D max). The wide range of values in some samples indicates a mottled or non-uniform appearance. Formulations and results are as tabulated below.

First coating composition:

1 As indicated.

The blue dye .may be added as a solution in methyl alcohol. The merocyanine spectral sensitizing dye is added as a solution in a small portion of the acetone. The water-insoluble solid o-alkyl-substitutedphenol reducing agent is present in an amount substantially stoichiometrically equivalent to the amount of silver salt.

TABLE IV Density of developed print, D min./ D max.

Mercurio acetate:

Contact prints of a photographic negative are made using a series of coated papers similarly prepared, exposing for three seconds using an incandescent filament light source which provides 300 foot-candles at the plane of the negative, and developing by holding the exposed sheet in close contact with a heated smooth metal surface at 235 F. for 25 seconds. The control sample containing no mercuric salt is completely and uniformly blackened. Prints having good contrast with dense black image areas are obtained at .05 and .10 percent of mercuric acetate. At larger percentages the density becomes observably less in both image and background areas.

Another control sample, i.e. containing no mercury, is similarly treated but with an exposure of one second and with a critical and very carefully controlled development time of ten seconds. A recognizable print with fair contrast is obtained, but the image areas have a brownish cast rather than the rich black appearance obtained with the longer development time.

EXAMPLE 3 Here the mercuric salt serves also as the source of the halide ion for the photosensitive catalyst-forming silver halide.

Composition A:

Silver behenate half soap 9.5 Polyvinyl butyral 11.4 Mercurio bromide .10 Methanol (solvent for HgBr2) .8 Acetone 32.8 Methylethylketone 26.8 Toluene 18.4 Sensitizing dye of Example 2 .0001 Composition B:

Cellulose acetate 1.0 Phthalazinone 2.4 Bis-(2 hydroxy,3 tertiarybutyl,5 methylphenyl)methane 2.0 Phthalic acid .05 Victoria Blue dye .001 Composition C 20.0 Acetone 54.5 Methanol 19.2 Composition C:

Cellulose acetate 5.0 Calcium carbonate powder 2.5 Silica powder 3.75 Polyvinyl acetate 10.0 Methanol 18.75 Acetone 60.0

Composition -A is applied at a coating weight, after drying, of 1.0 g./ sq. ft. and composition B at .30 g./sq. ft.

The sensitometric characteristics of coated paper prepared as thus described are determined by exposure, development, measurement of densities, and plotting of D log E curves. Values taken from these curves are compared with those obtained from sheet materials in which an equal molar proportion of calcium bromide is substituted for the mercuric bromide.

The results of the comparison are shown in the drawing, wherein FIG. l graphically represents the maximum and minimum densities developed in the two sheets at increasing times of development and at different temperatures,

FIG. 2 is a graph representing the values of gamma. obtained for the two sheets when developed for different times, and

lFIG. 3 indicates the relative photographic speeds of the two sheets.

As will be seen from FIG. l, the D min. or background density of the sheets made with calcium bromide increases very rapidly with increased time of development, Whereas a much slower rate of increase is obtained with the sheets containing mercury, so that useful prints may be obtained with the latter over a much wider range of development conditions. One result is a much higher available gamma, as shown in FIG. 2. Another is an orders-of-magnitude increase in photographic speed, observed in FIG. 3.

The components are mixed in a ball mill to provide uniform dispersion and the mixture is coated on paper at a thickness sucient to provide a coating weight of 1.0 \g./sq. ft. after drying.

The sheet is exposed in a sensitometer through a 0 to 3 optical density wedge for 10 seconds to tungsten lilament light at l95 foot-candles, and developed by heating for ten seconds at an optimum temperature of C. The optimum temperature is selected as that temperature which in ten seconds will produce a iirst faint visible dan-kening of the previously unexposed sheet.

Control sheets containing no mercury are similarly prepared and tested, the mercuric bromide being replaced by 10.15 part of cadmium bromide and by 0.16 part of barium bromide respectively, the optimum development temperature being 77 C. in each instance. As shown in Table V, both speed and maximum density are significantly increased in the presence of mercuric ion.

Where Examples 1-3 each employ two separate coatings in preparing the image-forming stratum, Example 4 uses a single mixture of all components and the stratum is produced in a single application. These coatings may be applied to paper, transparent flexible films or glass plates, or other suitable carriers or baokings. It is also possible to separate the components, for example by combining the photosensitive silver halide, the organic silver salt oxidizing agent, and the mercuric salt with a. suitable binder on a light-.sensitive sheet which `after exposure must then be heated in contact with a separately prepared developer sheet containing the organic reducing agent.

Silver bromide is a particularly useful silver halide photosensitive material but silver chloride and silver iodide, and mixed silver halides, are also useful. These materials may further be spectrally sensitized to any desired portion of the visible range of the spectrum by the addition of suitable sensitizers such as the merocyanne spectral sensitizing dyes. Various other modifications will be apparent to the skilled worker in the light of the foregoing description.

What is claimed is as follows:

1. Sheet material useful in the recording of light-images and including a stratum containing (a) photosensitive silver halide catalyst-forming means, (b) heat-sensitive reactant image-forming 'means including an organic silver salt oxidizing agent and a reducing agent for silver ion, the oxidation-reduction reaction of which to produce a visible change' is accelerated by said catalyst, and (o) a source of mercuric ion in significant small amount up to about .O7 mol of mercury per mol of silver.

2. Sheet material of claim 1 wherein the amount of mercury is between about .005 and about .05 mol per mol of silver.

3. Sheet material of claim 1 wherein the reducing agent is a normally solid, Water-insoluble, o-alkyl substituted phenol.

4. Sheet material of claim 1 wherein said stratum contains about one-half to about ten percent by Weight of phthalazinone.

5. Sheet material of claim 4 wherein the reducing agent is a normally solid, water-insoluble, o-alkyl substituted phenol.

6. Sheet material of claim 1 wherein said stratum is carried on a supporting substrate.

I'7. Sheet material of claim 6 wherein said substrate is paper.

8. Sheet material of claim 6 wherein said stratum and said substrate are transparent. i

9. Method of making a sheet material as deined in UNITED STATES PATENTS 3,218,166 11/ 1965 [Reitter 96-67 3,094,417 6/ 1963 Workman 96-28 3,408,438 11/ 1'968 Loklcen 96--95 3,107,174 10/ 1963 Wartman 117-3612 OTHER REFERENCES Rose, The Condensed Chemical Dictionary, 1965, p. 810.

NORMAN G. TORCHI'N, `Primary Examiner E. C. KI'MLIN, Assistant Examiner U.S. Cl. XR. 96-85, 87, 102 

